Cobalt catalyst comprising a support comprising a mixed oxide phase including cobalt and/or nickel produced from an organic compound from the family of carboyxyanhydrides

ABSTRACT

The present invention relates to a catalyst containing an active cobalt phase, deposited on a support comprising alumina, silica or silica-alumina, said support containing a mixed oxide phase containing cobalt and/or nickel, said catalyst has been prepared by introducing at least one organic compound of the family of carboxyanhydrides. The invention also relates to the process for the preparation thereof, and to the use thereof in the field of Fischer-Tropsch synthesis processes.

FIELD OF THE INVENTION

The invention relates to a catalyst containing an active cobalt phase,deposited on a support comprising alumina, silica or silica-alumina,said support containing a mixed oxide phase containing cobalt and/ornickel, said catalyst has been prepared by introducing at least oneorganic compound of the family of carboxyanhydrides. The invention alsorelates to the method for preparing same and to the use thereof in thefield of Fischer-Tropsch synthesis processes.

PRIOR ART

The Fischer-Tropsch synthesis processes make it possible to obtain awide range of hydrocarbon cuts from the CO+H₂ mixture, commonly referredto as synthesis gas or syngas.

The simplified stoichiometric equation (limited in the equation below tothe formation of alkanes) of the Fischer-Tropsch synthesis is written:nCO+(2n+1)H₂→C_(n)H_(2n+2) +nH₂O

The catalysts used in Fischer-Tropsch synthesis are usually supportedcatalysts based on alumina, silica or silica-alumina or combinations ofthese supports, the active phase mainly consisting of iron (Fe) orcobalt (Co) optionally doped with a noble metal such as platinum (Pt),rhodium (Rh) or rutherium (Ru).

The addition of an organic compound to Fischer-Tropsch catalysts toimprove their activity was recommended by a person skilled in the art.

Many documents describe the use of various ranges of organic compoundsas additives, such as nitrogen-containing organic compounds and/oroxygen-containing organic compounds.

In particular, U.S. Pat. Nos. 5,856,260 and 5,856,261 respectively teachthe introduction, during the preparation of the catalyst, of polyols ofgeneral formula CnH_(2n+2)O_(x) with n being an integer between 2 andaround 6, and x being an integer between 2 and 11 or sugars ofmonosaccharide or disaccharide type, sucrose being particularlypreferred.

Patent application US 2005/0026776 teaches the use of chelatingcompounds of the following types: nitrilotriacetic acid (NTA),trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CyDTA) orethylenediaminetetraacetic acid (EDTA), or else glycine, aspartic acidor citric acid for obtaining a catalyst with a reduced size of Co₃O₄crystallites. Other documents teach the use of polyethers (WO2014/092278 and WO 2015/183061), glyoxylic acid (WO 2015/183059),unsaturated dicarboxylic acids (US 2011/0028575) or else ofmultifunctional carboxylic acids of formula HOOC—(CRR¹)_(n)—COOH withn≥1 in the preparation of Fischer-Tropsch catalysts (WO 98/47618).

Patent application FR 3050659 describes the use of lactones, of linearmono- and diesters, and of cyclic carbonates in order to increase theactivity and the selectivity of catalysts for Fischer-Tropsch synthesis.

Document WO 2012/013866 discloses the use of a cyclic oligosaccharide,in particular cyclodextrin, as additive of a Fischer-Tropsch catalyst.This document also describes the use of a support based onsilica-alumina optionally containing a spinel.

Irrespective of the compounds selected, the induced modifications do notalways make it possible to increase the catalyst performance enough tomake the process profitable. Furthermore, it is often very complicatedto carry out the industrial deployment thereof as the methods arecomplex to implement.

Consequently, it appears essential, for catalyst manufacturers, to findnew catalysts for Fischer-Tropsch synthesis with improved performance.

AIMS AND SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a catalystcontaining an active cobalt phase, deposited on a support comprisingalumina, silica or silica-alumina, said support containing a mixed oxidephase containing cobalt and/or nickel, said catalyst being prepared by aprocess comprising at least:

a) a step of bringing a support comprising alumina, silica orsilica-alumina into contact with at least one solution containing atleast one precursor of cobalt and/or of nickel, then drying at atemperature below 200° C. and calcining at a temperature of between 700°C. and 1200° C., so as to obtain a mixed oxide phase containing cobaltand/or nickel in the support,

-   -   then carrying out

b) a step of bringing said support containing said mixed oxide phaseinto contact with at least one solution containing at least oneprecursor of cobalt,

c) a step of bringing said support containing said mixed oxide phaseinto contact with at least one organic compound of the family ofcarboxyanhydrides,

steps b) and c) being able to be performed separately, in any order, orat the same time,

d) then carrying out a step of drying at a temperature below 200° C.

Not one of the documents mentioned relating to the additives describes acobalt-based catalyst deposited on a support containing a mixed oxidephase containing cobalt and/or nickel prepared using an organic compoundof the family of carboxyanhydrides.

The applicant has indeed observed that the use of an organic compound ofthe family of carboxyanhydrides as an organic additive during thepreparation of a catalyst containing an active cobalt phase, depositedon a support comprising alumina, silica or silica-alumina, said supportalso containing a mixed oxide phase containing cobalt and/or nickel madeit possible to obtain a catalyst for Fischer-Tropsch synthesisdisplaying improved catalytic performance.

Indeed, the catalyst according to the invention displays increasedactivity and increased selectivity relative to catalysts containing amixed oxide phase containing cobalt and/or nickel in their support butprepared without additivation by an organic compound of the family ofcarboxyanhydrides or relative to additivated catalysts with no mixedoxide phase containing cobalt and/or nickel in the support. The use ofsuch an organic compound during the preparation of a cobalt-basedcatalyst comprising a support containing a mixed oxide phase containingcobalt and/or nickel seems to have a synergistic effect on the activityand selectivity in a Fischer-Tropsch process.

Without being bound to any theory, it was demonstrated that such acatalyst has a dispersion of the cobalt that is substantially greaterthan that exhibited by catalysts prepared in the absence of such anorganic compound. This results in the presence of a greater number ofactive sites for the catalysts prepared in the presence of at least oneorganic compound of the family of carboxyanhydrides, even if thiscarboxyanhydride compound is at least partially eliminated afterwards bya drying and optionally a calcining.

According to one variant, the content of mixed oxide phase in thesupport is between 0.1% and 50% by weight relative to the weight of thesupport.

According to one variant, the mixed oxide phase comprises an aluminateof formula CoAl₂O₄ or NiAl₂O₄ in the case of a support based on aluminaor on silica-alumina.

According to one variant, the mixed oxide phase comprises a silicate offormula Co₂SiO₄ or Ni₂SiO₄ in the case of a support based on silica oron silica-alumina.

According to one variant, the silica content of said support is between0.5% by weight and 30% by weight relative to the weight of the supportbefore the formation of the mixed oxide phase when the support is asilica-alumina.

According to one variant, the organic compound of the family ofcarboxyanhydrides is selected from O-carboxyanhydrides andN-carboxyanhydrides.

According to one variant, the organic compound of the family ofcarboxyanhydrides is selected from the group of O-carboxyanhydridesconsisting of 5-methyl-1,3-dioxolane-2,4-dione and2,5-dioxo-1,3-dioxolane-4-propanoic acid, or from the group ofN-carboxyanhydrides consisting of 2,5-oxazolidinedione and3,4-dimethyl-2,5-oxazolidinedione.

According to one variant, the molar ratio of organic compound of thefamily of carboxyanhydrides introduced during step c) relative to thecobalt element introduced in step b) is between 0.01 mol/mol and 2.0mol/mol.

According to one variant, the content of cobalt element introducedduring step b) as active phase is between 2% and 40% by weight expressedas cobalt metal element relative to the total weight of the catalyst.

According to one variant, the catalyst further comprises an elementselected from groups VIIIB, IA, IB, IIA, IIB, IIIA, IIIB and VA.

According to one variant, the catalyst further contains an additionalorganic compound other than the compound of the family ofcarboxyanhydrides, said additional organic compound containing oxygenand/or nitrogen, and preferably comprising one or more chemicalfunctions selected from a carboxylic, alcohol, ether, aldehyde, ketone,amine, nitrile, imide, oxime, urea and amide function.

According to one variant, after the drying step d), a calcining step e)is carried out at a temperature of between 200° C. and 550° C. in aninert atmosphere or in an oxygen-containing atmosphere.

According to one variant, the catalyst obtained in the drying step d) orobtained in the calcining step e) at a temperature of between 200° C.and 500° C., is reduced.

According to a second aspect, the invention also relates to a processfor preparing the catalyst according to the invention.

According to a third aspect, the invention also relates to the use ofthe catalyst according to the invention in a Fischer-Tropsch synthesisprocess wherein the catalyst according to the invention or prepared inaccordance with the invention is brought into contact with a feedstockcomprising synthesis gas under a total pressure of between 0.1 MPa and15 MPa, under a temperature of between 150° C. and 350° C., and at anhourly space velocity of between 100 and 20 000 volumes of synthesis gasper volume of catalyst and per hour with an H₂/CO molar ratio of thesynthesis gas of between 0.5 and 4.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, groups of chemical elements are given according to the CASclassification (CRC Handbook of Chemistry and Physics, published by CRCPress, Editor in Chief D. R. Lide, 81^(st) edition, 2000-2001). Forexample, group VIII according to the CAS classification corresponds tothe metals of columns 8, 9 and 10 according to the new IUPACclassification. Textural and structural properties of the support and ofthe catalyst described below are determined by the characterizationmethods known to a person skilled in the art. The total pore volume andthe pore distribution are determined in the present invention bynitrogen porosimetry as described in the book “Adsorption by powders andporous solids. Principles, methodology and applications”, written by F.Rouquérol, J. Rouquérol and K. Sing, Academic Press, 1999.

The specific surface area is understood to mean the BET specific surfacearea (SBFT in m²/g) determined by nitrogen adsorption in accordance withstandard ASTM D 3663-78 developed from the Brunauer-Emmett-Teller methoddescribed in the journal “The Journal of the American Chemical Society”,1938, 60 (309).

The catalyst according to the invention is a catalyst containing anactive cobalt phase, deposited on a support comprising alumina, silicaor silica-alumina, said support containing a mixed oxide phasecontaining cobalt and/or nickel, said catalyst being prepared by aprocess comprising at least:

a) a step of bringing a support comprising alumina, silica orsilica-alumina into contact with at least one solution containing atleast one precursor of cobalt and/or of nickel, then drying at atemperature below 200° C. and calcining at a temperature of between 700°C. and 1200° C., so as to obtain a mixed oxide phase containing cobaltand/or nickel in the support,

then carrying out

b) a step of bringing said support containing said mixed oxide phaseinto contact with at least one solution containing at least oneprecursor of cobalt,

c) a step of bringing said support containing said mixed oxide phaseinto contact with at least one organic compound of the family ofcarboxyanhydrides, steps b) and c) being able to be performedseparately, in any order, or at the same time,

d) then carrying out a step of drying at a temperature below 200° C.

The term “carboxyanhydrides” is understood to mean any cyclic organiccompound comprising a carboxyanhydride function, i.e. a —CO—O—CO—X— or—X—CO—O—CO— linkage within the ring with —CO— corresponding to acarbonyl function and X possibly being an oxygen or nitrogen atom. ForX═O reference is made to O-carboxyanhydride and when X═N reference ismade to N-carboxyanhydride.

The various steps of the process leading to the catalyst according tothe invention are described in detail in the following paragraphs.

Step a) Formation of the Mixed Oxide Phase Containing Cobalt and/orNickel

The objective of step a) is the formation of a mixed oxide phasecontaining cobalt and/or nickel in a support comprising alumina, silicaor silica-alumina by bringing it into contact with a solution containingat least one precursor of cobalt and/or of nickel, followed by a dryingand a high-temperature calcining.

It is known that the presence of a mixed oxide phase containing cobaltand/or nickel in an alumina, silica or silica-alumina support makes itpossible to improve the resistance to the phenomenon of chemical andmechanical attrition in a Fischer-Tropsch process, and therefore tostabilize the support.

The formation of the mixed oxide phase in the support, often referred toas the support stabilization step, may be carried out by any methodknown to a person skilled in the art. It is generally carried out byintroducing cobalt and/or nickel in the form of a salt precursor, forexample of nitrate type, over the initial support containing alumina,silica or silica-alumina. By calcining at very high temperature, themixed oxide phase containing cobalt and/or nickel is formed andstabilizes the whole of the support. The cobalt and/or nickel containedin the mixed oxide phase cannot be reduced during the final activationof the Fischer-Tropsch (reduction) catalyst. The cobalt and/or nickelcontained in the mixed oxide phase does (do) not therefore constitutethe active phase of the catalyst.

According to step (a), a step is carried out of bringing a supportcomprising alumina, silica or silica-alumina into contact with at leastone solution containing at least one precursor of cobalt and/or ofnickel, then drying and calcining at a temperature of between 700° C.and 1200° C., so as to obtain a mixed oxide phase containing cobaltand/or nickel in the support.

More particularly, the contacting step a) may be carried out byimpregnation, preferably dry impregnation, of a support comprisingalumina, silica or silica-alumina, preformed or in powder form, with atleast one aqueous solution containing the precursor of cobalt and/or ofnickel, followed by a drying and a calcining at a temperature between700° C. and 1200° C.

The cobalt is brought into contact with the support by means of anycobalt precursor that is soluble in the aqueous phase. Preferably, thecobalt precursor is introduced in aqueous solution, for example innitrate, carbonate, acetate or chloride form, in the form of complexesformed with acetylacetonates or of any other inorganic derivativesoluble in aqueous solution, which is brought into contact with saidsupport. The cobalt precursor advantageously used is cobalt nitrate orcobalt acetate.

The nickel is brought into contact with the support by means of anynickel precursor that is soluble in the aqueous phase. Preferably, saidnickel precursor is introduced in aqueous solution, for example innitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate oroxalate form, in the form of complexes formed with acetylacetonates orof any other inorganic derivative soluble in aqueous solution, which isbrought into contact with said support. The nickel precursoradvantageously used is nickel nitrate, nickel chloride, nickel acetateor nickel hydroxycarbonate.

The total content of cobalt and/or of nickel is advantageously between1% and 20% by weight and preferably between 2% and 10% by weightrelative to the total mass of the final support.

The drying is carried out at a temperature below 200° C., and preferablyabove 60° C. The drying time may range from 30 minutes to three hours.

The calcining is carried out at a temperature between 700° C. and 1200°C., preferably between 850° C. and 1200° C., and preferably between 850°C. and 900° C., generally for a period of between one hour and 24 hoursand preferably between 2 hours and 5 hours. The calcining is generallycarried out under an oxidizing atmosphere, for example in air, or inoxygen-depleted air; it may also be carried out at least partly undernitrogen. It makes it possible to convert the precursors of cobaltand/or of nickel and the alumina and/or silica into the mixed oxidephase containing cobalt and/or nickel.

According to one variant, the calcining may also be carried out in twosteps, said calcining is advantageously carried out at a temperaturebetween 300° C. and 600° C. in air for a period of between half an hourand three hours, and then at a temperature between 700° C. and 1200° C.,preferably between 850° C. and 1200° C. and preferably between 850° C.and 900° C., generally for a period of between one hour and 24 hours,and preferably of between 2 hours and 5 hours.

The support comprises alumina, silica or silica-alumina.

When the support comprises alumina, it contains more than 50% by weightof alumina relative to the weight of the support before the formation ofthe mixed oxide phase and, preferably, it contains only alumina. Thealumina may be present in a crystallographic form of gamma-, delta-,theta- or alpha-alumina type, taken alone or as a mixture.

In another preferred case, the support comprises silica. In this case,it contains more than 50% by weight of silica relative to the weight ofthe support before the formation of the mixed oxide phase and,preferably, it contains only silica. Sources of silicon are well knownto a person skilled in the art.

In another preferred case, the support comprises a silica-alumina. Asupport comprising a silica-alumina is understood to mean a support inwhich the silicon and the aluminum are in the form of agglomerates ofsilica or alumina respectively, amorphous aluminosilicate or any othermixed phase containing silicon and aluminum, it being understood thatthe support is not mesostructured. A mesostructured support isunderstood to mean a support comprising pores having a uniform diameterof between 2 nm and 50 nm, preferably distributed homogeneously andregularly, also referred to as “organized” porosity at the scale of theparticle. Preferably, the alumina and the silica are present in the formof a mixture of oxides SiO₂—Al₂O₃. The silica content in thesilica-alumina support varies from 0.5% by weight to 30% by weight,preferably from 1% by weight to 25% by weight, and more preferably stillfrom 1.5% to 20% by weight relative to the weight of the support beforethe formation of the mixed oxide phase.

According to one preferred variant, the support consists, before theformulation of the mixed oxide phase, of alumina, silica orsilica-alumina, and particularly preferably the support consists, beforethe formulation of the mixed oxide phase, of silica-alumina.

The support also contains a mixed oxide phase containing cobalt and/ornickel. A mixed oxide phase containing cobalt and/or nickel isunderstood to mean a phase in which cations of cobalt and/or of nickelare combined with the O²⁻ oxide ions of the alumina and/or silicasupport thus forming a mixed phase containing aluminates and/orsilicates containing cobalt and/or nickel. The mixed oxide phase may bein amorphous form or in crystalline form.

When the support is based on alumina, the mixed oxide phase may comprisean aluminate of formula CoAl₂O₄ or NiAl₂O₄, in amorphous or crystallineform, for example in spinel form.

When the support is based on silica, the mixed oxide phase may comprisea silicate of formula Co₂SiO₄ or Ni₂SiO₄ (cobalt- ornickelorthosilicate), in amorphous or crystalline form.

When the support is based on silica-alumina, the mixed oxide phase maycomprise an aluminate of formula CoAl₂O₄ or NiAl₂O₄ in amorphous orcrystalline form, for example in spinel form, and/or a silicate offormula Co₂SiO₄ or Ni₂SiO₄, in amorphous or crystalline form.

Generally, the content of the mixed oxide phase in the support isbetween 0.1% and 50% by weight relative to the support, preferablybetween 0.5% and 30% by weight, and more preferably between 1% and 20%by weight.

The presence of a mixed oxide phase in the catalyst according to theinvention is measured by Temperature-Programmed Reduction (or TPR) suchas for example described in Oil & Gas Science and Technology, Rev. IFP,Vol. 64 (2009), No. 1, pp. 11-12. According to this technique, thecatalyst is heated in a stream of a reducing agent, for example in astream of dihydrogen. The measurement of the dihydrogen consumed as afunction of the temperature gives quantitative information regarding thereducibility of the species present. The presence of a mixed oxide phasein the catalyst is thus expressed by a consumption of dihydrogen at atemperature above around 800° C.

The support may have a morphology in the form of beads, extrudates (forexample of trilobe or quadrilobe shape) or pellets, especially when saidcatalyst is used in a reactor operating as a fixed bed, or may have amorphology in the form of a powder of variable particle size, especiallywhen said catalyst is used in a bubble-column (or “slurrybubble-column”) reactor. The size of the grains of the catalyst may bebetween a few microns and a few hundred microns. For a “slurry” reactorimplementation, the size of the particles of the catalyst ispreferentially between 10 microns and 500 microns, preferably between 10microns and 300 microns, very preferably between 20 microns and 200microns, and even more preferably between 30 microns and 160 microns.

The specific surface area of the support containing the mixed oxidephase is generally between 50 m²/g and 500 m²/g, preferably between 100m²/g and 300 m²/g, more preferably between 150 m²/g and 250 m²/g. Thepore volume of said support is generally between 0.3 ml/g and 1.2 ml/g,and preferably between 0.4 ml/g and 1 ml/g.

Thus, at the end of said step a), said support comprising alumina,silica or silica-alumina further comprises a mixed oxide phasecontaining cobalt and/or nickel.

Steps b) and c): Introduction of the Active Phase and Introduction ofthe Carboxyanhydride Compound

After the formation of the mixed oxide phase, the following steps arecarried out in the preparation of the catalyst according to theinvention:

b) a step of bringing said support containing said mixed oxide phaseinto contact with at least one solution containing at least oneprecursor of cobalt,

c) a step of bringing said support containing said mixed oxide phaseinto contact with at least one organic compound of the family ofcarboxyanhydrides steps b) and c) being able to be performed separately,in any order, or at the same time.

Step b)

Step b) of bringing said support into contact with at least one solutioncontaining at least one cobalt precursor may be carried out by anymethod well known to a person skilled in the art. Said step b) ispreferentially carried out by impregnation of the support by at leastone solution containing at least one cobalt precursor. In particular,said step b) can be achieved by dry impregnation, by excessimpregnation, or else by deposition-precipitation (as described in U.S.Pat. Nos. 5,874,381 and 6,534,436) according to methods well known to aperson skilled in the art. Preferably, said step b) is carried out bydry impregnation, which consists in bringing the catalyst support intocontact with a solution containing at least one cobalt precursor, thevolume of which is equal to the pore volume of the support to beimpregnated. This solution contains the cobalt precursor at the desiredconcentration.

The cobalt is brought into contact with said support by means of anycobalt precursor which is soluble in the aqueous phase or in the organicphase. When introduced in organic solution, said cobalt precursor is forexample cobalt acetate. Preferably, said cobalt precursor is introducedin aqueous solution, for example in nitrate, carbonate, acetate orchloride form, in the form of complexes formed with acetylacetonates orof any other inorganic derivative soluble in aqueous solution, which isbrought into contact with said support. Use is advantageously made, ascobalt precursor, of cobalt nitrate or cobalt acetate.

The content of cobalt element is between 2% and 40% by weight,preferably between 5% and 30% by weight, and more preferably between 10%and 25% by weight expressed as cobalt metal element relative to thetotal weight of the catalyst.

The catalyst may advantageously further comprise at least one elementselected from an element from groups VIIIB, IA, IB, IIA, IIB, IIIA, IIIBand/or VA. Such an element may act as cobalt promoter, making itpossible to improve the activity and/or the selectivity of the catalyst.

The preferred possible elements from group VIIIB are platinum, rutheniumand rhodium. The preferred elements from group IA are sodium andpotassium. The preferred elements from group IB are silver and gold. Thepreferred elements from group IIA are manganese and calcium. Thepreferred element from group IIB is zinc. The preferred elements fromgroup IIIA are boron and indium. The preferred elements from group IIIBare lanthanum and cerium. The preferred element from group VA isphosphorus.

The content of possible element from groups VIIIB, IA, IB, IIA, IIB,IIIA, IIIB and/or VA is between 50 ppm and 20% by weight, preferablybetween 100 ppm and 15% by weight, and more preferably between 100 ppmand 10% by weight expressed as element relative to the total weight ofthe catalyst.

According to one variant, when the catalyst contains one or severaladditional elements from groups VIIIB, IA, IB, IIA, IIB, IIIA, IIIBand/or VA, this or these elements may be either initially present on thesupport before the preparation of the catalyst, or introduced at anymoment of the preparation and by any method known to a person skilled inthe art.

Step c)

Bringing the organic compound of the family of carboxyanhydrides usedfor the implementation of said step c) into contact with said support isachieved by impregnation, in particular by dry impregnation or excessimpregnation, preferentially by dry impregnation. Said organic compoundpreferentially is impregnated on said support after solubilization in anaqueous solution

The organic compound of the family of carboxyanhydrides is a cyclicorganic compound comprising a carboxyanhydride function, i.e. a—CO—O—CO—X— or —X—CO—O—CO— linkage within the ring with —CO—corresponding to a carbonyl function and X possibly being an oxygen ornitrogen atom. For X═O reference is made to O-carboxyanhydride and whenX═N reference is made to N-carboxyanhydride.

According to the invention, one or more organic compounds of the familyof carboxyanhydrides as described below may be used for theimplementation of step c).

The organic compound of the family of carboxyanhydrides may be selectedfrom O-carboxyanhydrides and N-carboxyanhydrides, which are substitutedor unsubstituted.

According to one variant, the organic compound of the family ofcarboxyanhydrides is selected from O-carboxyanhydrides. The only carbonatom of the ring not involved in the O-carboxyanhydride function may bemonosubstituted or disubstituted by one or more linear, branched orcyclic, aliphatic, unsaturated or aromatic hydrocarbon radicalscomprising from 1 to 15 carbon atoms and which may comprise one or moreheteroatoms such as oxygen, nitrogen or halogen. According to thisvariant, the organic compound of the family of carboxyanhydrides ispreferably chosen from 5-methyl-1,3-dioxolane-2,4-dione or2,5-dioxo-1,3-dioxolane-4-propanoic acid.

According to one variant, the organic compound of the family ofcarboxyanhydrides is selected from N-carboxyanhydrides. The carbon ofthe ring not involved in the N-carboxyanhydride function may bemonosubstituted or disubstituted by one or more linear, branched orcyclic, aliphatic, unsaturated or aromatic hydrocarbon radicalscomprising from 1 to 15 carbon atoms and which may comprise one or moreheteroatoms such as oxygen, nitrogen or halogen. The nitrogen of thering may be substituted by a proton or a linear, branched or cyclic,aliphatic, unsaturated or aromatic hydrocarbon radical comprising from 1to 15 carbon atoms and which may comprise one or more heteroatoms suchas oxygen, nitrogen or halogen. According to this variant, the organiccompound of the family of carboxyanhydrides is preferably selected from2,5-oxazolidinedione or 3,4-dimethyl-2,5-oxazolidinedione.

Advantageously, the organic compound of the family of carboxyanhydridesis selected from 5-methyl-1,3-dioxolane-2,4-dione,2,5-dioxo-1,3-dioxolane-4-propanoic acid, 2,5-oxazolidinedione and3,4-dimethyl-2,5-oxazolidinedione.

The molar ratio of organic compound(s) of the family ofcarboxyanhydrides introduced during step c) relative to the cobaltelement introduced in step b) is preferably between 0.01 and 2.0mol/mol, preferably between 0.05 and 1.0.

The catalyst according to the invention may comprise, in addition to theorganic compound of the family of carboxyanhydrides, an additionalorganic compound or a group of additional organic compounds, other thanthe compound of the family of carboxyanhydrides, and known for theirrole as additives. The function of the additives is to increase thecatalytic activity relative to non-additivated catalysts. In particular,the catalyst according to the invention may further comprise one or moreadditional oxygen-containing and/or nitrogen-containing organiccompounds, other than the compound of the family of carboxyanhydrides.

Generally, the additional organic compound comprises one or morechemical functions selected from a carboxylic, alcohol, ether, aldehyde,ketone, amine, nitrile, imide, oxime, urea and amide function.

The additional oxygen-containing organic compound may comprise one ormore chemical functions selected from a carboxylic, alcohol, ether,aldehyde or ketone function. By way of example, the oxygen-containingorganic compound may be selected from the group consisting of ethyleneglycol, diethylene glycol, triethylene glycol, a polyethylene glycol(with a molecular weight between 200 and 1500 g/mol), propylene glycol,2-butoxyethanol, 2-(2-butoxyethoxy)ethanol, 2-(2-methoxyethoxy)ethanol,triethylene glycol dimethyl ether, glycerol, acetophenone,2,4-pentanedione, pentanone, acetic acid, maleic acid, malic acid,malonic acid, oxalic acid, gluconic acid, tartaric acid, citric acid,succinic acid, γ-ketovaleric acid, γ-valerolactone, 4-hydroxyvalericacid, 2-pentenoic acid, 3-pentenoic acid, 4-pentenoic acid, a C1-C4dialkyl succinate, methyl acetoacetate, dibenzofuran, a crown ether,orthophthalic acid and glucose.

The additional nitrogen-containing organic compound may comprise one ormore chemical functions selected from an amine or nitrile function. Byway of example, the nitrogen-containing organic compound may be one ormore selected from the group consisting of ethylenediamine,diethylenetriamine, hexamethylenediamine, triethylenetetramine,tetraethylenepentamine, pentaethylenehexamine, acetonitrile, octylamine,guanidine or a carbazole.

The additional organic compound containing oxygen and nitrogen maycomprise one or more chemical functions selected from a carboxylic,alcohol, ether, aldehyde, ketone, amine, nitrile, imide, amide, urea oroxime function. By way of example, the organic compound containingoxygen and nitrogen may be selected from the group consisting of1,2-cyclohexanediaminetetraacetic acid, monoethanolamine (MEA),N-methylpyrrolidone, dimethylformamide, ethylenediaminetetraacetic acid(EDTA), alanine, glycine, proline, lysine, nitrilotriacetic acid (NTA),N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA),diethylenetriaminepentaacetic acid (DPTA), tetramethylurea, glutamicacid, dimethylglyoxime, bicine or tricine, or else a lactam.

The total molar ratio of additional oxygen-containing and/ornitrogen-containing organic compound(s) other than the organic compoundcomprising the family of carboxyanhydrides relative to the cobaltelement introduced in step b) is preferably between 0.01 mol/mol and 2mol/mol, preferably between 0.1 mol/mol and 2 mol/mol, preferablybetween 0.2 and 1.5 mol/mol, calculated on the basis of the componentsintroduced into the impregnating solution(s).

When the catalyst further contains an additional organic compound otherthan the organic compound of the family of carboxyanhydrides, thisadditional organic compound may be either initially present on thesupport before the preparation of the catalyst, or incorporated into thecatalyst at any moment of the preparation and by any method known to aperson skilled in the art.

Implementations of Steps b) and c)

The process for preparing the catalyst according to the invention, inparticular with respect to steps b) and c), comprises several modes ofimplementation. They are distinguished in particular by the moment whenthe organic compound is introduced, which may be carried out either atthe same time as the impregnation of the cobalt of the active phase(co-impregnation) or after the impregnation of the cobalt of the activephase (post-impregnation), or before the impregnation of the cobalt ofthe active phase (pre-impregnation). In addition, it is possible tocombine the modes of implementation.

A first mode of implementation consists in carrying out said steps b)and c) simultaneously so that said organic compound and at least saidcobalt precursor present in the active phase are co-impregnated on saidsupport (co-impregnation). Said first mode of implementationadvantageously comprises the implementation of one or more steps b). Inparticular, one or more steps b) advantageously precede(s) and/orfollow(s) said co-impregnation step. Said first mode of implementationmay comprise several co-impregnation steps.

A second mode of implementation consists in carrying out said step b)prior to said step c) (post-impregnation). In accordance with saidsecond mode of implementation, one or more steps b) of bringing intocontact at least the cobalt present in the active phase of the catalystprecede(s) said step c).

A third mode of implementation consists in carrying out said step c)prior to said step b) (pre-impregnation). Advantageously, said step c)is followed by several steps b).

When steps b) and c) are carried out separately (post-impregnation orpre-impregnation), a drying step is advantageously carried out betweenthe impregnation steps. The intermediate drying step is carried out at atemperature below 200° C., advantageously between 50 and 180° C.,preferably between 70 and 150° C., very preferably between 75 and 130°C. and optionally a maturation period was observed between theimpregnation step and the intermediate drying step.

Each of the three modes of implementation described above may be carriedout independently so that the catalyst according to the invention isprepared either according to said first mode of implementation, oraccording to said second mode of implementation or else according tosaid third mode of implementation. However, it may be advantageous tocombine said first mode with said second mode or with said third mode:both the cobalt present in the active phase and the organic compound aredeposited at least twice on the catalyst support, namely at least onceby co-impregnation and at least once by successive impregnation.

Advantageously, after each impregnation step, whether this is a cobaltor organic compound impregnation step, the impregnated support is leftto mature. Maturing allows the impregnation solution to be dispersedhomogeneously within the support.

Any maturing step described in the present invention is advantageouslycarried out at atmospheric pressure, in a water-saturated atmosphere andat a temperature between 17° C. and 50° C., and preferably at roomtemperature. Generally, a maturing time of between ten minutes andforty-eight hours, and preferably of between thirty minutes and fivehours, is sufficient. Longer periods of time are not ruled out but donot necessarily contribute an improvement.

Any impregnation solution described in the present invention maycomprise any polar solvent known to a person skilled in the art. Saidpolar solvent used is advantageously selected from the group formed bymethanol, ethanol, water, phenol, cyclohexanol, taken alone or as amixture. Said polar solvent may also be advantageously selected from thegroup formed by propylene carbonate, DMSO (dimethyl sulfoxide),N-methylpyrrolidone (NMP) or sulfolane, taken alone or as a mixture.Preferably, use is made of a polar protic solvent A list of common polarsolvents and also their dielectric constant can be found in the book“Solvents and Solvent Effects in Organic Chemistry” C. Reichardt,Wiley-VCH, 3rd edition, 2003, pages 472-474. Very preferably, thesolvent used is water or ethanol, and particularly preferably, thesolvent is water. In one possible embodiment, the solvent may be absentin the impregnation solution.

When several impregnation steps are carried out, each impregnation stepis preferably followed by an intermediate drying step at a temperaturebelow 200° C., advantageously between 50° C. and 180° C., preferablybetween 70° C. and 150° C., very preferably between 75° C. and 130° C.and optionally a maturation period was observed between the impregnationstep and the intermediate drying step.

Drying Step d)

In accordance with the drying step d) of the implementation for thepreparation of the catalyst, prepared according to at least one mode ofimplementation described above, the drying is carried out at atemperature below 200° C., advantageously between 50° C. and 180° C.,preferably between 70° C. and 150° C., very preferably between 75° C.and 130° C. The drying step is preferentially carried out for a periodof between 1 hour and 4 hours, preferably in an inert atmosphere or inan oxygen-containing atmosphere.

The drying step can be carried out by any technique known to a personskilled in the art. It is advantageously carried out at atmosphericpressure or at reduced pressure. Preferably, this step is carried out atatmospheric pressure. It is advantageously carried out in a crossed bedusing hot air or any other gas. Preferably, when the drying is carriedout in a fixed bed, the gas used is either air, or an inert gas such asargon or nitrogen. Very preferably, the drying is carried out in acrossed bed in the presence of nitrogen and/or air. Preferably, thedrying step has a short duration of between 5 minutes and 4 hours,preferably of between 30 minutes and 4 hours and very preferably ofbetween 1 hour and 3 hours.

According to a first variant, the drying is conducted so as to keeppreferably at least 10% of the organic compound of the family ofcarboxyanhydrides introduced during an impregnation step, preferablythis amount is greater than 30% and even more preferably greater than50%, calculated on the basis of the carbon remaining on the catalyst.When an organic compound containing oxygen and/or nitrogen other thanthe organic compound of the family of carboxyanhydrides is present, thedrying step is carried out so as to keep preferably at least 10%,preferably at least 30%, and very preferably at least 50% of the amountintroduced, calculated on the basis of carbon remaining on the catalyst.

At the end of the drying step d), a dried catalyst is then obtained,which will be subjected to an activation step for the subsequent usethereof in Fischer-Tropsch synthesis.

According to another variant, at the end of the drying step d), acalcining step e) is carried out at a temperature of between 200° C. and550° C., preferably of between 250° C. and 500° C., in an inertatmosphere (nitrogen for example) or in an oxygen-containing atmosphere(air for example). The duration of this heat treatment is generallybetween 0.5 hours and 16 hours, preferably between 1 hour and 5 hours.After this treatment, the cobalt of the active phase is thus in oxideform and the catalyst contains no more or very little organic compoundintroduced during synthesis thereof. However the introduction of theorganic compound during the preparation thereof has made it possible toincrease the dispersion of the active phase thus leading to a moreactive and/or more selective catalyst.

Activation (Reduction)

Prior to its use in the catalytic reactor and the implementation of theFischer-Tropsch process according to the invention, the dried catalystobtained in step d) or the calcined catalyst obtained in step e)advantageously undergoes a reductive treatment, for example with pure ordilute hydrogen, at high temperature. This treatment makes it possibleto activate said catalyst and to form particles of cobalt metal in thezero-valent state. The temperature of this reductive treatment ispreferentially between 200° C. and 500° C. and the duration thereof isbetween 2 hours and 20 hours.

This reductive treatment is carried out either in situ (in the samereactor as the one where the Fischer-Tropsch reaction is carried outaccording to the process of the invention), or ex situ before beingloaded into the reactor.

Process for Preparing the Catalyst

The invention also relates to the process for preparing the catalyst,the steps of which have been described in detail above.

Fischer-Tropsch Process

A final subject of the invention is the use of the catalyst according tothe invention in a Fischer-Tropsch synthesis process.

The Fischer-Tropsch process according to the invention leads to theproduction of essentially linear and saturated C5+ hydrocarbons (havingat least 5 carbon atoms per molecule). The hydrocarbons produced by theprocess of the invention are thus essentially paraffinic hydrocarbons,the fraction of which having the highest boiling points can be convertedwith a high yield to middle distillates (diesel and kerosene cuts) by ahydroconversion process such as catalytic hydrocracking and/orhydroisomerization.

The feedstock used for the implementation of the process of theinvention comprises synthesis gas. Synthesis gas is a mixture comprisingin particular carbon monoxide (CO) and hydrogen (H₂) having H₂/CO molarratios that may vary in a ratio of 0.5 to 4 depending on the process bywhich it was obtained. The H₂/CO molar ratio of the synthesis gas isgenerally close to 3 when the synthesis gas is obtained from thehydrocarbon or alcohol steam reforming process. The H₂/CO molar ratio ofthe synthesis gas is preferably of the order of 1.5 to 2 when thesynthesis gas is obtained from a partial oxidation process. The H₂/COmolar ratio of the synthesis gas is generally close to 2.5 when it isobtained from a thermal reforming process. The H₂/CO molar ratio of thesynthesis gas is generally close to 1 when it is obtained from a processfor gasification and reforming of CO₂.

The catalyst used in the hydrocarbon synthesis process according to theinvention may be implemented in various types of reactors, for examplefixed-bed, moving-bed, ebullated-bed or else three-phase fluidized-bedreactors. The implementation of the catalyst suspended in a three-phasefluidized reactor, preferentially of bubble column type, is preferred.In this preferred implementation of the catalyst, said catalyst isdivided in the form of a very fine powder, particularly of the order ofa few tens of microns, this powder forming a suspension with thereaction medium. This technology is also known under the “slurry”process terminology by a person skilled in the art.

The hydrocarbon synthesis process according to the invention isperformed under a total pressure of between 0.1 MPa and 15 MPa,preferably between 0.5 MPa and 10 MPa, under a temperature of between150° C. and 350° C., preferably between 180° C. and 270° C. The hourlyspace velocity is advantageously between 100 and 20 000 volumes ofsynthesis gas per volume of catalyst and per hour (100 to 20 000 h⁻¹)and preferably between 400 and 10 000 volumes of synthesis gas pervolume of catalyst and per hour (400 to 10 000 h⁻¹).

The following examples demonstrate the gains in performance regardingthe catalysts according to the invention.

EXAMPLES Example 1 (Comparative): Catalyst a of Formula Co/Al₂O₃

A catalyst A comprising cobalt deposited on an alumina support isprepared by dry impregnation of an aqueous solution of cobalt nitrate soas to deposit, in two successive steps, around 10% by weight of Co on agamma-alumina powder (PURALOX® SCCa 5/170, SASOL) having a mean particlesize equal to 80 μm, a surface area of 165 m²/g and a pore volumemeasured by nitrogen adsorption isotherm of 0.4 ml/g.

After a first dry impregnation, the solid is dried in a crossed bed at120° C. for 3 h in air and then calcined at 400° C. for 4 h in a crossedbed under a stream of air. The intermediate catalyst contains around 6%by weight of Co. It is subjected to a second step of dry impregnationusing a solution of cobalt nitrate. The solid obtained is dried in acrossed bed at 120° C. for 3 h in air and then calcined at 400° C. for 4h in a crossed bed under a stream of air. The final catalyst A isobtained which contains 10.5% by weight of Co (in CO₃O₄ oxide form).

Example 2 (Comparative): Catalyst B of Formula Co/Al₂O₃.SiO₂

A catalyst B comprising cobalt deposited on a silica-alumina support isprepared by dry impregnation of an aqueous solution of cobalt nitrate soas to deposit, in one step, around 10% by weight of Co on asilica-alumina initially containing 5% by weight of SiO₂ and having aspecific surface area of 180 m²/g and a pore volume of 0.8 ml/g.

After the dry impregnation, the solid is dried in a crossed bed at 120°C. for 3 h in air and then calcined at 400° C. for 4 h in a crossed bed.The final catalyst B is obtained which contains 9.9% by weight of Co (inCO₃O₄ oxide form).

Example 3 (Comparative): Catalyst C of Formula Co/CoAl₂O₄—Al₂O₃.SiO₂

A catalyst C comprising cobalt deposited on a support, based on a mixedoxide phase (in spinel form) included in a silica-alumina, is preparedby dry impregnation of an aqueous solution of cobalt nitrate so as todeposit, in one step, around 10% by weight of cobalt on the support.

The spinel present in the support of the catalyst C is a simple spinelformed of cobalt aluminate, which is included in a silica-aluminacontaining 5% by weight of SiO₂, and having a specific surface area of180 m²/g and a pore volume of 0.8 ml/g. The preparation of the spinelincluded in the silica-alumina is carried out by dry impregnation of anaqueous solution of cobalt nitrate so as to introduce 5% by weight of Cointo said silica-alumina. After drying at 120° C. for 3 hours, the solidis calcined at 850° C. for 4 hours in air. The support for the catalystdenoted by C′ is formed of 5% by weight of cobalt in the form of cobaltaluminate (i.e. 15% by weight of spinel) in the silica-alumina.

The cobalt-based active phase is then deposited on said support in onestep, by dry impregnation, according to a protocol that is identical tothat described for the preparation of catalyst B. The drying andcalcining steps are also performed under the same operating conditionsas those of example 2. The concentration of cobalt in the solution ofcobalt nitrate, used for the successive impregnations, is chosen inorder to obtain the catalyst C with the desired final Co content.

The final catalyst C has a total cobalt content of 15.7% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 10.7% by weight.

Example 4 (Comparative): Catalyst D of Formula Co/CoAl₂O₄—Al₂O₃.SiO₂Containing Citric Acid (Co-Impregnation)

A catalyst D comprising cobalt and citric acid deposited on a support,based on a spinel included in a silica-alumina, is prepared by dryimpregnation of an aqueous solution of cobalt nitrate and of citric acidso as to deposit around 10% by weight of cobalt on the support.

The cobalt-based active phase is deposited on the support C′ of example3 in one step, by dry impregnation of a solution containing cobaltnitrate and citric acid (Sigma Aldrich®, >99%) in a citric acid: Comolar ratio of 0.5. After dry impregnation, the solid undergoes amaturation in a water-saturated atmosphere for 9 hours at roomtemperature and then is dried in a crossed bed at 120° C. for 3 h inair, and then treated under nitrogen at 400° C. for 4 h in a crossedbed.

The final catalyst D has a total cobalt content of 14.1% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 9.1% by weight.

Example 5 (Comparative): Catalyst E of Formula Co/CoAl₂O₄—I₂O₃.SiO₂Containing Citric Acid (Post-Impregnation)

A catalyst E comprising cobalt and citric acid deposited on a support,based on a spinel included in a silica-alumina, is prepared by dryimpregnation of an aqueous solution of cobalt nitrate, and then of anaqueous solution of citric acid so as to deposit around 10% by weight ofcobalt on the support.

The cobalt-based active phase is deposited on the support C′ of example3 in one step, by dry impregnation of a solution containing cobaltnitrate. After dry impregnation, the solid undergoes drying in a crossedbed at 120° C. for 3 h in air.

In a second step, the citric acid is deposited on the preceding solid inone step, by dry impregnation of a solution containing citric acid(Sigma Aldrich®, >99%) at a concentration for attaining a citric acid:Co molar ratio of 0.5 on the final catalyst. After dry impregnation, thesolid undergoes a maturation in a water-saturated atmosphere for 9 hoursat room temperature and then is dried in a crossed bed at 120° C. for 3h in air, and then treated under nitrogen at 400° C. for 4 h in acrossed bed.

The final catalyst E has a total cobalt content of 14.0% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 9.0% by weight.

Example 6 (According to the Invention): Catalyst F of FormulaCo/CoAl₂O₄—Al₂O₃.SiO₂ Containing 5-methyl-1,3-dioxolane-2,4-dione

A catalyst F comprising cobalt and 5-methyl-1,3-dioxolane-2,4-dionedeposited on a support, based on a spinel included in a silica-alumina,is prepared by dry impregnation of an aqueous solution of cobaltnitrate, and then of an ethanolic solution of5-methyl-1,3-dioxolane-2,4-dione so as to deposit around 10% by weightof cobalt on the support.

The cobalt-based active phase is deposited on the support C′ of example3 in one step, by dry impregnation of a solution containing cobaltnitrate. After dry impregnation, the solid undergoes drying in a crossedbed at 120° C. for 3 h in air.

In a second step the 5-methyl-1,3-dioxolane-2,4-dione is deposited onthe preceding solid in one step, by dry impregnation of an ethanolicsolution containing 5-methyl-1,3-dioxolane-2,4-dione (AccelPharmtech®, >95-98%) at a concentration for attaining a5-methyl-1,3-dioxolane-2,4-dione: CO molar ratio of 0.5 on the finalcatalyst. After dry impregnation, the solid undergoes a maturation in awater-saturated atmosphere for 9 hours at room temperature and then isdried in a crossed bed at 120° C. for 3 h in air, and then treated undernitrogen at 400° C. for 4 h in a crossed bed.

The final catalyst F has a total cobalt content of 14.6% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 9.6% by weight.

Example 7 (According to the Invention): Catalyst G of FormulaCo/CoAl₂O₄—Al₂O₃.SiO₂ Containing 2,5-dioxo-1,3-dioxolane-4-propanoicAcid

A catalyst G comprising cobalt and 2,5-dioxo-1,3-dioxolane-4-propanoicacid deposited on a support, based on a spinel included in asilica-alumina, is prepared by dry impregnation of an aqueous solutionof cobalt nitrate, and then of an ethanolic solution of2,5-dioxo-1,3-dioxolane-4-propanoic acid so as to deposit around 10% byweight of cobalt on the support.

The cobalt-based active phase is deposited on the support C′ of example3 in one step, by dry impregnation of a solution containing cobaltnitrate. After dry impregnation, the solid undergoes drying in a crossedbed at 120° C. for 3 h in air.

In a second step, the 2,5-dioxo-1,3-dioxolane-4-propanoic acid isdeposited on the preceding solid in one step, by dry impregnation of anethanolic solution containing 2,5-dioxo-1,3-dioxolane-4-propanoic acid(prepared in accordance with Chem. Commun. 2008, 1786-1788) at aconcentration for attaining a 2,5-dioxo-1,3-dioxolane-4-propanoic acid:Co molar ratio of 0.5 on the final catalyst. After dry impregnation, thesolid undergoes a maturation in a water-saturated atmosphere for 9 hoursat room temperature and then is dried in a crossed bed at 120° C. for 3h in air, and then treated under nitrogen at 400° C. for 4 h in acrossed bed.

The final catalyst G has a total cobalt content of 14.9% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 9.9% by weight.

Example 8 (According to the Invention): Catalyst H of FormulaCo/CoAl₂O₄—Al₂O₃.SiO₂ Containing 2,5-oxazolidinedione

A catalyst H comprising cobalt and 2,5-oxazolidinedione deposited on asupport, based on a spinel included in a silica-alumina, is prepared bydry impregnation of an aqueous solution of cobalt nitrate, and then ofan ethanolic solution of 2,5-oxazolidinedione so as to deposit around10% by weight of cobalt on the support.

The cobalt-based active phase is deposited on the support C′ of example3 in one step, by dry impregnation of a solution containing cobaltnitrate. After dry impregnation, the solid undergoes drying in a crossedbed at 120° C. for 3 h in air.

In a second step, the 2,5-oxazolidinedione is deposited on the precedingsolid in one step, by dry impregnation of an ethanolic solutioncontaining 2,5-oxazolidinedione (Merck®, 95-98%) at a concentration forattaining a 2,5-oxazolidinedione: Co molar ratio of 0.5 on the finalcatalyst. After dry impregnation, the solid undergoes a maturation in awater-saturated atmosphere for 9 hours at room temperature and then isdried in a crossed bed at 120° C. for 3 h in air, and then treated undernitrogen at 400° C. for 4 h in a crossed bed.

The final catalyst H has a total cobalt content of 14.6% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 9.6% by weight.

Example 9 (According to the Invention): Catalyst I of Formula:Co/CoAl₂O₄—Al₂O₃.SiO₂ Containing 3,4-dimethyl-2,5-oxazolidinedione

A catalyst I comprising cobalt and 3,4-dimethyl-2,5-oxazolidinedionedeposited on a support, based on a spinel included in a silica-alumina,is prepared by dry impregnation of an aqueous solution of cobaltnitrate, and then of an ethanolic solution of3,4-dimethyl-2,5-oxazolidinedione, so as to deposit around 10% by weightof cobalt on the support.

The cobalt-based active phase is deposited on the support C′ of example3 in one step, by dry impregnation of a solution containing cobaltnitrate. After dry impregnation, the solid undergoes drying in a crossedbed at 120° C. for 3 h in air.

In a second step, the 3,4-dimethyl-2,5-oxazolidinedione is deposited onthe preceding solid in one step, by dry impregnation of an ethanolicsolution containing 3,4-dimethyl-2,5-oxazolidinedione (Merck®, 95-98%)at a concentration for attaining a 3,4-dimethyl-2,5-oxazolidinedione: Comolar ratio of 0.5 on the final catalyst. After dry impregnation, thesolid undergoes a maturation in a water-saturated atmosphere for 9 hoursat room temperature and then is dried in a crossed bed at 120° C. for 3h in air, and then treated under nitrogen at 400° C. for 4 h in acrossed bed.

The final catalyst J has a total cobalt content of 14.7% by weight (thecontent of Co present in the spinel phase being included) and a contentof cobalt in CO₃O₄ oxide form of 9.7% by weight.

Example 10 (According to the Invention): Catalyst J of FormulaCo/CoAl₂O₄—Al₂O₃.SiO₂ Containing 5-methyl-1,3-dioxolane-2,4-dione

The catalyst J is prepared in a manner similar to the catalyst F exceptthat it does not undergo a heat treatment under nitrogen at 400° C. atthe end of the preparation.

Example 11: Catalytic Performance of Catalysts a to J in Fischer-TropschReaction

The catalysts A, B, C, D, E, F, G, H, I and J, before being tested inFischer-Tropsch synthesis, are reduced in situ under a stream of purehydrogen at 400° C. for 16 hours. The Fischer-Tropsch synthesis reactionis performed in a fixed-bed tubular reactor operating continuously.

Each of the catalysts is in powder form with a diameter of between 40microns and 150 microns.

The test conditions are as follows:

Temperature=216° C.

Total pressure=2 MPa

Hourly space velocity (HSV)=4100 NL/h⁻¹/kg catalyst

H₂/CO molar ratio=2/1

The results, expressed in terms of activity (conversion of CO in %) andselectivity (weight percentage of C₈ ₊ hydrocarbons over all of theproducts formed), appear in table 1.

Conversion of C₈ ⁺ selectivity at CO at 70 h 70 h under under reactionreaction stream Catalyst stream (%) (% by weight) A (comparative) 27.557.1 B (comparative) 38.1 65.9 C (comparative) 44.7 68.0 D (comparative)30.8 53.3 E (comparative) 41.3 56.1 F (invention) 63.1 71.8 G(invention) 62.3 70.4 H (invention) 57.6 67.5 I (invention) 59.7 68.0 J(invention) 65.2 71.9

The results in table 1 show that the catalysts according to theinvention are more active and/or more selective than the catalysts knownfrom the prior art.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding French application No. 18/71.303,filed Oct. 25, 2018, are incorporated by reference herein.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

APPENDIX

The table below lists examples of organic compounds of the family ofcarboxyanhydrides cited in the present description and the structuralformulae thereof.

Name Formula 5-methyl-1,3-dioxolane-2,4-dione

2,5-dioxo-1,3-dioxolane-4- propanoic acid

2,5-oxazolidinedione

3,4-dimethyl-2,5-oxazolidinedione

The invention claimed is:
 1. A process for preparing a catalystcontaining an active cobalt phase, deposited on a support comprisingalumina, silica or silica-alumina, said support containing a mixed oxidephase containing cobalt and/or nickel, said process comprising: a)bringing a support comprising alumina, silica or silica-alumina intocontact with at least one solution containing at least one precursor ofcobalt and/or of nickel, then drying at a temperature below 200° C. andcalcining at a temperature of between 700° C. and 1200° C., so as toobtain a mixed oxide phase containing cobalt and/or nickel in thesupport, then b) bringing said support containing said mixed oxide phaseinto contact with at least one solution containing at least oneprecursor of cobalt, c) bringing said support containing said mixedoxide phase into contact with at least one organic compound that is anO-carboxyanhydride that is 5-methyl-1,3-dioxolane-2,4-dione or2,5-dioxo-1,3-dioxolane-4-propanoic acid, or an N-carboxyanhydride thatis 2,5-oxazolidinedione or 3,4-dimethyl-2,5-oxazolidinedione, b) and c)being able to be performed separately, in any order, or at the sametime, and d) optionally then drying at a temperature below 200° C. 2.The process as claimed in claim 1, wherein the content of mixed oxidephase in the support is between 0.1% and 50% by weight relative to theweight of the support.
 3. The process as claimed in claim 1, wherein themixed oxide phase comprises an aluminate of formula CoAl₂O₄ or NiAl₂O₄in the case of a support based on alumina or on silica-alumina.
 4. Theprocess as claimed in claim 1, wherein the mixed oxide phase comprises asilicate of formula Co₂SiO₄ or Ni₂SiO₄ in the case of a support based onsilica or on silica-alumina.
 5. The process as claimed in claim 1,wherein the silica content of said support is between 0.5% by weight and30% by weight relative to the weight of the support before the formationof the mixed oxide phase when the support is a silica-alumina.
 6. Theprocess as claimed in claim 1, wherein the organic compound is5-methyl-1,3-dioxolane-2,4-dione or 2,5-dioxo-1,3-dioxolane-4-propanoicacid.
 7. The process as claimed in claim 1, wherein the molar ratio oforganic compound of the family of carboxyanhydrides introduced during c)relative to the cobalt element introduced in b) is 0.01 mol/mol to 2.0mol/mol.
 8. The process as claimed in claim 1, wherein the content ofcobalt element introduced during b) as active phase is 2% to 40% byweight expressed as cobalt metal element relative to the total weight ofthe catalyst.
 9. The process as claimed in claim 1, wherein the catalystfurther comprises an element of groups VIIIB, IA, IB, IIA, IIB, IIIA,IIIB or VA, present initially on the support before preparation of thecatalyst or introduced at any point during preparation of the catalyst.10. The process as claimed in claim 1, wherein the catalyst furthercontains an additional organic compound other than the compound of thefamily of carboxyanhydrides, said additional organic compound containingoxygen and/or nitrogen, said additional organic compound being initiallypresent on the support before preparation of the catalyst or introducedat any point during preparation of the catalyst.
 11. The process asclaimed in claim 1, wherein, after drying in d), calcining e) is carriedout at a temperature of 200° C. to 550° C. in an inert atmosphere or inan oxygen-containing atmosphere.
 12. The process as claimed in claim 11,wherein the catalyst obtained in drying d) or obtained in calcining e)is reduced.
 13. The process according to claim 10, wherein theadditional organic compound comprises one or more chemical functionsthat is a carboxylic, alcohol, ether, aldehyde, ketone, amine, nitrile,imide, oxime, urea or amide function.